25 year experiment shows ants can break down minerals, sequester CO2

And that reaction pulls carbon dioxide out of the atmosphere.

If you want a role model for work ethic in the animal kingdom, you’d do well to pick the ant. Maintaining tunnels, gathering food, and defending the colony are all in a solid day’s work. Now you might be able to cross off another item on the ant to-do list: pulling carbon dioxide out of the atmosphere.

Over geologic timescales, the Earth has a convenient regulator on its thermostat: the weathering of many minerals. During their breakdown, they react with carbon dioxide, which converts them into a clay mineral while also producing carbonate. In a warmer climate, weathering ramps up, removing more CO2 from the atmosphere. This provides a cooling influence. In a cooler climate, weathering slows and CO2 can accumulate in the atmosphere, nudging temperatures upwards.

Some of this is simply the result of physical weathering of exposed rock at the surface, but living organisms contribute as well. Tree roots penetrate cracks and pry rocks apart. Lichens and fungi in soil slowly dissolve rock. Burrowing things move material around.

Quantifying the influence of biology is a real challenge. Some things, like vegetation, have been studied but we remain ignorant about the weathering work done by many other organisms. Among the ones we've been ignorant about? Ants.

Arizona State’s Ronald Dorn has made a career studying weathering. Before that career started, he got some advice. “Luna Leopold was a famous geomorphologist at Cal Berkeley when I was a master’s student,” Dorn told Ars. “I had a couple of classes form Luna, and he urged us all to start baseline experiments when we started a new job as faculty. He said that geomorphology has few such long-term data gathering projects and that it would be important.”

So a little over 25 years ago, he crushed up a batch of Hawaiian basalt into fresh sand and found interesting places to bury it. That included sites in the Catalina Mountains of Arizona and at Palo Duro Canyon in Texas. The basalt sand went into half-meter holes augered into a variety of environments including bare ground, tree roots, and ant nests—with sand left in an open plastic pipe as a baseline.

Every five years, Dorn collected samples of the sand. With 25 years of samples in hand, he analyzed the amount of weathering the sand grains had undergone by throwing them under an electron microscope and calculating the amount of dissolution that had taken place. Because the weathering reaction also produces carbonate, the amount of carbonate was also measured at each location.

To Dorn’s surprise, the material from the ant nests stood out. Sand placed among tree roots experienced about 10 to 40 times as much weathering as the baseline grains, confirming that trees and their symbiotic fungi help break down minerals. In the ant nests, however, weathering was more like 50 to 175 times the baseline. Yet samples from termite nests were at the low end of the tree root range.

The ant nests also accumulated carbonate over time, while the bare ground sites didn’t. That could corroborate the high rate of weathering, but it’s also possible that other chemistry going on inside the nest contributes to carbonate formation.

Nobody has really studied mineral weathering in ant nests before, so we don’t actually know how this accelerated weathering is being accomplished. About all we can say is that ants do move bits of soils to and fro, which would mix the sand grains around. Dorn notes that these ants seem to be doing exactly what we would like to do—convert atmospheric carbon dioxide into minerals underground. It’s possible that the ants may have some tips for us if we could learn what’s going on in those nests.

Dorn also notes, very speculatively, that ants diversified and multiplied over the same time period that atmospheric CO2 declined from the hot climate of the dinosaurs into the ice age of the last few million years. Given their prodigious talents for weathering, it’s at least possible that ants had a little something to do with it.